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### Constructing a Secondary Datum Line

You can construct a Secondary Datum Line from a plane, line, or set of points. The set of points can be multiple selected points, a constructed set of points, or a scan feature that contains multiple points.

The secondary datum construction uses the points within the input feature (or features) as well as the plane from the primary datum input to create an "orientation constrained" and "external to material" 2D line. You can use this line in alignments to simulate a secondary datum feature.

- "Orientation constrained" means that the input points are forced perpendicular to the primary datum.

- "External to material" means that the resulting line contacts the highest point or points from the input feature (or features), subject to the orientation constraint and the selected math type.

PC-DMIS constructs the secondary datum line in the plane that you select as the primary datum.

Examples

The examples below show the points as if viewed from the selected plane.

- Constrained MinMax is the default math type specified by the ISO 1101 standard.

- Constrained L2 is the default math type specified by the ASME Y14.5 standard.

L∞

The red line is the L∞ plane targeting the external envelope (constrained MinMax type in PC-DMIS)

L2

The green line is the constrained L2 plane targeting the external envelope (constrained L2 math type in PC-DMIS)

How to Construct a Secondary Datum Line

1. Access the Construct Line dialog box (Insert | Feature | Constructed | Line).

2. From drop-down list that has Auto selected, select Secondary Datum.

3. From the list of features, select the input feature (or features). For valid input feature types, see the table in the "Constructing a Line Feature" topic above.

4. From the Primary datum area, from the drop-down list, select the primary datum. This datum can be either a plane from the measurement routine, or a workplane from the active alignment.

5. From the Math Type area, from the first drop-down list, select the math type (CONSTRAINED_L2 or CONSTRAINED_MINMAX)

6. From the Math Type area, from the second drop-down list, select a probe compensation option (BF for best fit or BFRE for best fit recompensate).

7. Click the Create button to insert the constructed line feature into your measurement routine.